'Display - Appearance' option settings
The Display option within the editor's Popup Settings box contains 5 option tabs. From left to right, they include:
This article focuses on the 'Display' >> 'Appearance' option settings within the Popup Settings box.
Display >> Appearance option
The 'Popup Theme' option menu provides 6 popup themes to choose among. The plugin default option is set to 'Default Theme'. See the article 'Popup Theme Editor Introduction' on how to customize popup themes. The 'Customize This Theme' link within the settings box redirects to the Popup Theme Editor for the 'Default Theme'.